JP3409891B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly to temporarily storing evaporated fuel in a canister,
The present invention relates to an air-fuel ratio control device for an internal-combustion engine, which realizes excellent air-fuel ratio control in an internal-combustion engine including an evaporation purge system that purges the internal-combustion engine under a predetermined operating condition.

[0002]

2. Description of the Related Art In an internal combustion engine, the highest combustion efficiency and good exhaust emission are obtained when the supplied mixture has a stoichiometric air-fuel ratio. For this reason, air-fuel ratio control of the air-fuel mixture has been generally performed conventionally in the vehicle-mounted internal combustion engine that requires these characteristics at a particularly high level.

In this air-fuel ratio control, the intake air amount is calculated based on the volume and temperature of the air taken into the internal combustion engine, and the theoretical air-fuel ratio (14: 1 in the case of gasoline is calculated with respect to the calculated air amount. The fuel is supplied to the intake passage of the internal combustion engine in an amount calculated so that (near) can be realized.

On the other hand, in-vehicle internal combustion engines are generally equipped with an evaporative purge system which prevents the fuel vapor generated in the fuel tank from being released into the atmosphere when the internal combustion engine is stopped at a high temperature. ing.

The above-mentioned evaporative purging system has a passage (vapor passage) for introducing steam generated in a fuel tank, a canister that contains activated carbon and communicates with the vapor passage, and a passage (purge passage for communicating the canister and the intake passage). )When,
The fuel vapor generated in the fuel tank is temporarily adsorbed in the canister, and the adsorbed fuel is appropriately purged into the intake passage after the internal combustion engine is started.

Therefore, in an internal combustion engine having an evaporative purge system, even if the internal combustion engine stops at high temperature and the fuel vapor is generated due to the residual heat, the generated fuel vapor remains until the internal combustion engine is started. It is adsorbed and held by the activated carbon in the canister. Then, the fuel is appropriately purged from the canister after the internal combustion engine is started, and is appropriately consumed as fuel.

When performing the air-fuel ratio control as described above in an internal combustion engine having such an evaporative purge system, it is necessary to calculate the fuel supply amount in consideration of the fuel to be purged. If such correction is not performed, the fuel to be purged will be wasted as excess fuel, resulting in a problem such as deterioration of tail pipe emission.

For this reason, the present applicant has filed Japanese Patent Application No. 4-1745.
As disclosed also in No. 24, in an air-fuel ratio control device for an internal combustion engine, which is generally equipped with an evaporative purge system, it is premised that the fuel purge rate (purge flow rate / intake air amount) is constant and that purge is not performed. A correction process is performed in which the fuel supply amount calculated as is multiplied by a constant correction coefficient according to the purge rate.

Here, the constant purge rate control is executed in the evaporative purge system because the purge fuel is always supplied to the internal combustion engine at a constant rate regardless of the amount of intake air, as described above. This is because the desired fuel supply amount correction can be realized simply by multiplying the correction coefficient, and the calculation process thereof is simple.

The internal combustion engine described in the above publication is a device capable of executing a constant purge rate control and having a mechanism for actually measuring the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine.
Further, in order to learn changes with time of the internal combustion engine and the evaporative purge system, a plurality of purge rates are appropriately set, the air-fuel ratio is measured, and a correction coefficient is learned and corrected as appropriate.

As described above, even if the internal combustion engine is provided with the evaporative purge system and the fuel is purged from the canister, if the purge flow rate can be appropriately controlled in relation to the intake air amount, the intake passage It is possible to execute appropriate air-fuel ratio control by appropriately reducing the amount of fuel supplied to the inside.

[0012]

In the conventional air-fuel ratio control device, the control mechanism for controlling the conduction of the purge passage is appropriately driven to obtain the desired purge rate.
That is, when the air-fuel ratio control by the constant purge rate control is being executed, the control mechanism is driven so as to increase or decrease the purge flow rate according to the increase or decrease in the intake air amount.

In this case, the calculation process of the fuel supply amount in the air-fuel ratio control device is performed only by multiplying the intake air amount by an amount capable of realizing the stoichiometric air-fuel ratio by a constant correction coefficient as described above. It is executed immediately after detecting the air amount.

On the other hand, the purge flow rate does not change until the control mechanism responds to the change after the intake air amount is detected, that is, until the response time of the control mechanism elapses.
Further, even after the response of the control mechanism, the substantial purge flow rate does not change until the purge fuel that has passed through the control mechanism actually reaches the internal combustion engine. Further, even if the state of the control mechanism changes, the desired purge flow rate does not flow until the state of the canister follows the change and reaches the equilibrium state.

Therefore, in the above conventional air-fuel ratio control device, the purge flow rate could not follow the fluctuation of the intake air amount, and the constant purge rate may not be established in the transient state. As a result, when the intake air amount largely fluctuates, immediately after that, the air-fuel mixture supplied to the internal combustion engine largely deviates from the stoichiometric air-fuel ratio, and there arises a problem that exhaust emission temporarily deteriorates.

Further, in an internal combustion engine in which the fuel injection amount is electronically controlled, for example, when the throttle valve is suddenly closed under a situation where the engine speed exceeds a predetermined speed, the purpose is to improve fuel economy. However, the deterioration of exhaust emission at the time of fuel cut is also a problem in an internal combustion engine equipped with an evaporative purge system.

That is, in the case of executing the fuel cut in the internal combustion engine, it is general to cut the fuel after a predetermined delay time has elapsed after the throttle valve is closed rapidly in order to mitigate the impact due to the fuel cut. Then, in the internal combustion engine provided with the evaporative purge system, the purging of fuel is stopped at the start timing of this fuel cut.

In this case, as described above, between the command value issued to the control mechanism for controlling the purge flow rate and the purge flow rate actually supplied to the internal combustion engine, the response delay of the control mechanism and the flow of the purge fuel flow. There is a gap due to time, and when fuel is cut, especially when fuel is being purged at a high purge rate, the fuel temporarily becomes rich due to the gap, which causes deterioration of exhaust emission. It was.

The present invention has been made in view of the above-mentioned points, and estimates the ratio of the fuel purged from the canister to the mixture drawn into the internal combustion engine, and based on the estimated value. By correcting the fuel injection amount by
Alternatively, by setting the delay time at the time of fuel cut of the internal combustion engine to be shorter as the purge rate is higher, or in an internal combustion engine equipped with a dashpot mechanism to mitigate the impact at the time of rapid closing of the throttle valve, at the time of rapid closing of the throttle valve. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can solve the above problems by increasing the amount of air flowing through the dashpot as the purge rate increases.

[0020]

1 to 3 are diagrams showing the principle configuration of an air-fuel ratio control system for an internal combustion engine capable of achieving the above object. That is, as shown in FIG. 1, the above object is to provide a canister 1 for temporarily storing evaporated fuel, and a target purge flow rate calculation means 3 for calculating a purge flow rate to be purged into the intake passage 2 according to the operating condition of the internal combustion engine. And an evaporative purge system 6 including purge flow rate control means 5a and 5b for controlling the purge flow rate by controlling the conduction of a purge passage 4 that connects the canister 1 and the intake passage 2 with each other. In an air-fuel ratio control device for an internal combustion engine, which injects fuel according to the amount of air taken into the internal combustion engine into the intake passage 2 by means of fuel injection means 7a, 7b . The above
Based on the conduction state of over-di passages, Ru is sucked into the internal combustion engine
The actual purge rate estimating means M1 for estimating the ratio of purged fuel in the mixed Aiki, depending on the purge ratio estimated by said actual purge rate estimating means M1, so that the desired air-fuel ratio is realized
And an air-fuel ratio control device for an internal combustion engine, which further comprises a fuel injection amount calculation means M2 for correcting the fuel injection amount by the fuel injection means.

Further, as shown in FIG. 2, the above-mentioned object is a target for calculating a canister 1 for temporarily storing evaporated fuel and an amount of purge fuel to be purged into the intake passage 2 in accordance with the operating condition of the internal combustion engine. An evaporative purge system 6 including a purge flow rate calculation means 3 and purge flow rate control means 5a and 5b for controlling the purge flow rate by controlling the conduction of a purge passage 4 that connects the canister 1 and the intake passage 2 is provided. A device for controlling the air-fuel ratio of an internal combustion engine,
Fuel injection means 7a, 7b for injecting fuel into the intake passage 2 according to the amount of air taken into the internal combustion engine, and the purge flow rate control means 5a, 5b and the fuel injection means 7a, when a predetermined condition is satisfied. In the air-fuel ratio control device for an internal combustion engine, which includes a fuel cut command means 8 for commanding a fuel supply cut to 7b, a purge rate estimating means M3 for estimating a ratio of purge fuel in the air-fuel mixture, and an internal combustion engine After the operating state detecting means M4 for detecting that the operating state for executing the cut is detected and the operating state for executing the fuel cut by the operating state detecting means M4, the estimation by the purge rate estimating means M3 is performed. According to the purge rate, the larger the purge rate is, the longer the delay time set to a shorter time elapses, and then the condition determination means M5 determines whether the execution condition of the fuel cut is satisfied.
It is also solved by an air-fuel ratio control device for an internal combustion engine, which comprises:

Further, as shown in FIG. 3, a canister 1 for temporarily storing evaporated fuel, and a target purge flow rate calculating means 3 for calculating the amount of purge fuel to be purged into the intake passage 2 in accordance with the operating condition of the internal combustion engine. And a purge flow rate control means 5 for controlling the purge flow rate by controlling the continuity of the purge passage 4 that connects the canister 1 and the intake passage 2 to each other.
The evaporative purge system 6 including a and 5b is provided, and when the throttle valve provided in the intake passage 2 is suddenly closed, an appropriate amount of air is supplied to prevent a sudden decrease in the intake air amount. Dashpot mechanism 9a, 9 for circulation
In an air-fuel ratio control device for an internal-combustion engine for controlling the air-fuel ratio of an internal-combustion engine, the purge-rate estimating means M3 for estimating the ratio of the purged fuel in the air-fuel mixture and the throttle valve when the throttle valve is suddenly closed are used. The air-fuel ratio control device for an internal combustion engine, which is also provided with a circulating air amount varying means M6 that sets a larger amount of air to be circulated by the dashpot mechanisms 9a and 9b as the estimated value of the purge rate estimating means M3 is larger, has the above-mentioned object. Effective to achieve.

[0023]

In the air-fuel ratio control system for an internal combustion engine according to the first aspect of the present invention, when the purge passage 4 is turned on or off by the purge flow rate control means 5a, 5b during operation of the internal combustion engine, the conduction or The intake negative pressure in the intake passage is supplied to the canister 1 in response to the interruption.

Therefore, when the fuel corresponding to the supplied negative pressure is purged from the canister 1 and the evaporative purge system 6 reaches a steady state, the target purge flow rate calculating means 3 is provided in the intake passage 2. The amount of fuel calculated in step 1 is purged.

The actual purge rate estimating means M1 is independent of the calculation result of the target purge flow rate calculating means 3 and is based on the conduction state of the purge passage a predetermined time before.
Then, the actual purge ratio is estimated from the ratio of the purge fuel in the air-fuel mixture sucked into the internal combustion engine at the present moment . Therefore, when the intake air amount transiently changes, the actual purge rate in which the operation delay of the evaporative purge system 6 is taken into consideration is estimated.

As a result, in the fuel injection amount calculation means M2, regardless of whether the intake air amount transiently fluctuates or is in a steady state, the air-fuel mixture actually sucked into the internal combustion engine is stoichiometric air-fuel ratio. The amount of fuel in the vicinity is calculated, and the amount of fuel that can always realize an appropriate air-fuel ratio is supplied from the fuel injection means 7a, 7b.

According to the second aspect of the invention, the condition determining means M5 executes the fuel cut after a predetermined delay time after the operating condition detecting means M4 detects the operating condition in which the fuel cut should be executed. Determine if the condition is met. Then, when the condition is satisfied, the fuel cut command means 8 issues a fuel cut command, and the supply of fuel is stopped in the purge flow rate control means 5a, 5b and the fuel injection means 7a, 7b.

In this case, the delay time set by the condition determining means M5 is set based on the estimated value of the purge rate estimating means M3, and a large amount is set when the internal combustion engine is in a state where fuel cut should be executed. If the purge fuel is supplied, the delay time is short, and if the purge fuel is small, the delay time is set long.

Therefore, when the purge rate is low and the purged fuel does not significantly affect the operating state of the internal combustion engine, a delay time sufficient to absorb the impact during fuel cut is secured, and the purge rate is high. Is high and a large amount of purge fuel is supplied to the internal combustion engine after fuel cut,
By setting the delay time short, deterioration of exhaust emission due to excessive fuel supply is effectively prevented.

Further, in the invention according to claim 3, when the throttle valve is suddenly closed, the dashpot mechanism 9
Based on the functions of a and 9b, an appropriate amount of air then flows through the intake passage 2. At this time, the amount of air flowing through the dashpots 9a, 9b is the amount set by the circulating air amount varying means M6 based on the estimated value of the purge rate estimating means M3, and the larger the purge rate, the greater the amount. Is set.

Therefore, when the throttle valve is suddenly closed, the amount of purge fuel actually supplied to the internal combustion engine cannot follow the rapid closure, but the amount of air corresponding to the amount or concentration of the purge fuel is increased. Is ensured, the enrichment of the air-fuel ratio is prevented, and good exhaust emission is ensured.

[0032]

FIG. 4 is an overall configuration diagram of an internal combustion engine 10 equipped with an air-fuel ratio control system according to an embodiment of the present invention. In the figure, 11 is an engine body, 12 is an intake manifold, 1
Reference numeral 3 indicates an exhaust manifold, and 14 indicates a fuel injection valve attached to each intake branch pipe 12.

Each intake branch pipe 12 has a common surge tank 15
The surge tank 15 is connected to an air cleaner 18 via an intake duct 16. Intake duct 16
A throttle valve 19 is provided therein, and a surge tank 15 is provided with an intake pressure sensor 17 for measuring an intake pipe internal pressure for estimating an intake air amount.

Further, the internal combustion engine 10 has an evaporative purge system 22. In the figure, reference numeral 21 denotes a canister that constitutes the evaporation purge system 22, and the canister 2
Activated carbon 20 is built in the unit 1. Canister 21
Has a fuel vapor chamber 23a and an atmosphere chamber 23b on both sides of the activated carbon 20, respectively. The fuel vapor chamber 23 a is connected to the fuel tank 25 via the vapor passage 24 on the one hand, and is connected to the surge tank 15 via the purge passage 26 on the other hand.

A purge control valve 27, which is controlled by the output signal of the electronic control unit 30, is provided in the purge passage 26. Further, the fuel vapor generated in the fuel tank 25 is sent into the canister 21 via the purge passage 24 and adsorbed on the activated carbon 20.

When the purge control valve 27 is opened, air is sent from the atmospheric chamber 23b into the purge passage 26 through the activated carbon 20. When the air passes through the activated carbon 20, the fuel vapor adsorbed on the activated carbon 20 is separated from the activated carbon 20, and the air containing the fuel vapor is discharged into the surge tank 15 through the purge passage 26.

The electronic control unit 30 is composed of a digital computer, and a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, a B-RAM which are mutually connected by a bidirectional bus 31. (Backup-random access memory) 46, input port 35, and output port 3
6 is provided.

The intake pressure sensor 17 provided in the surge tank 15 detects the pressure in the intake pipe, and its output signal is A /
It is input to the input port 35 via the D converter 37. A throttle switch 38 that is turned on when the throttle valve 19 is at the idling opening is attached to the throttle valve 19, and an output signal of the throttle switch 38 is input to the input port 35.

Here, the pressure in the surge tank 15 during operation of the internal combustion engine 10 is atmospheric pressure as the opening degree of the throttle valve 19 increases, that is, as the intake air amount supplied to the internal combustion engine 10 increases. Near the throttle valve 1
The smaller the opening of 9 and the smaller the amount of intake air, the more negative the pressure becomes. That is, the detected value of the intake pressure sensor 17 is the internal combustion engine 1
A value corresponding to an intake air amount of 0 is shown.

A water temperature sensor 39 for generating an output voltage proportional to the engine cooling water temperature is attached to the engine body 11, and the output voltage of the water temperature sensor 39 is input to the input port 35 via the A / D converter 40. . An air-fuel ratio sensor (O ₂ sensor) 41 is attached to the exhaust manifold 13, and an output signal of the air-fuel ratio sensor 41 is input to the input port 35 via the A / D converter 42.

Further, the input port 35 is connected to a crank angle sensor 43 which generates an output pulse each time the crankshaft rotates, for example, 30 ° CA. The CPU 34 calculates the engine speed (NE) based on this output pulse. On the other hand, the output port 36 is the corresponding drive circuit 4
4, 45 through the fuel injection valve 14 and the purge control valve 27.
Connected to.

In the air-fuel ratio control device according to the present invention, as described above, the target purge flow rate calculation means 3, the purge flow rate control means 5a, 5b, the fuel injection means 7a, 7b, the actual purge rate estimation means M1, the fuel injection amount calculation are performed. It is configured by means M2 and the like. Of these, a part (5a) of the purge flow rate control means and a part (7a) of the fuel injection means are constituted by the purge control valve 27 and the fuel injection valve 14, respectively.

The components other than these are realized by the electronic control unit 30 executing the programs to be described later stored in the ROM 32. Hereinafter, the content of the processing executed by the electronic control unit 30 and the operation of the apparatus of this embodiment accompanying it will be described.

Here, the apparatus according to the present embodiment estimates the ratio of the purged fuel in the air-fuel mixture when the fuel is purged from the canister 1 so that the intake air amount changes transiently. Is also characterized in that an appropriate air-fuel ratio can be secured. This function is performed by the CPU 34 in the purge control routine shown in FIG. 5 and the fuel injection time TA shown in FIG.
This is demonstrated by executing the U correction routine.

Hereinafter, these routine processes will be described in detail. Prior to this, the air-fuel ratio feedback control which is the basis of the air-fuel ratio control in the present embodiment will be briefly described with reference to FIGS. 9 and 10. .

FIG. 9 shows a flow chart of the main part of the air-fuel ratio feedback control executed by the electronic control unit 30 based on the output signal of the O ₂ sensor 41. Here, the air-fuel ratio feedback control is to detect the air-fuel ratio of the air-fuel mixture actually supplied to the internal combustion engine 10 on the basis of the oxygen concentration signal emitted from the O ₂ sensor 41, and to bring the air-fuel ratio close to the theoretical air-fuel ratio. This is a control for correcting the fuel injection amount.

When such air-fuel ratio control is executed, the air-fuel ratio control device is remarkably different from the air-fuel ratio control device which only sets the reference fuel injection amount calculated as the theoretical air-fuel ratio can be calculated in accordance with the intake air amount. Excellent air-fuel ratio accuracy can be secured.

The specific processing contents will be described below with reference to FIG. The routine shown in the figure is an interrupt routine for multiplying a reference fuel injection amount calculated corresponding to the intake air amount to calculate a feedback correction coefficient FAF that realizes an appropriate correction. It is the one that is activated.

When the routine shown in FIG. 9 is started, first, at step 300, the air-fuel ratio signal V emitted by the O ₂ sensor 41 is detected. As described above, based on the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 10, the internal combustion engine 1
This is because the air-fuel ratio of the air-fuel mixture actually supplied to 0 is detected.

When the air-fuel ratio signal V is detected, step 30
In step 2, it is determined whether the value of the air-fuel ratio signal V is higher than the voltage E representing the target air-fuel ratio. This is to determine whether the actual air-fuel ratio is fuel rich or fuel lean.

Then, when V> E (when it is lean with respect to the target air-fuel ratio), the routine proceeds to step 304, where it is judged if it was lean at the previous interruption. This is to determine whether the lean detected this time is continuous lean or lean after reversal from rich.

If it was not lean at the time of the previous interruption, it is judged that the state is reversed from rich to lean, and step 3
Proceed to 06, the feedback correction coefficient FAF at this point
Is stored as FAFR, the process proceeds to step 308, the skip value S is added to FAF, and the process of this step ends.

On the other hand, when it is determined in step 304 that the side is lean even at the time of the previous interruption,
Proceeding to step 310, the FAF has a predetermined step value K (K
<< S) is added and the processing of this time is ended.

Therefore, when the air-fuel ratio of the exhaust gas reverses from rich to lean as shown in FIG.
At time t ₁ during the middle, the feedback correction coefficient FAF is rapidly increased by the skip value S (step 3 above).
04-308). Then, if the fuel lean state continues thereafter (period in FIG. 10), FAF is gradually increased as the step value K is added.

On the other hand, in step 302, V> E
Is not established (the air-fuel ratio of the exhaust gas is rich), the routine proceeds to step 312, where it is judged whether or not it was rich at the time of the previous interruption. If it is not rich at the time of the previous interruption, it is determined that the lean state has been changed to rich, and the routine proceeds to step 314.

At step 314, the feedback correction coefficient FAF at this time is stored as FAFL. Then, in step 316, the skip value S is subtracted from FAF, and the processing of this time is ended. On the other hand, if it is determined in step 312 that the fuel was rich even at the time of the previous interruption, the process proceeds to step 318 and F
The step value K is subtracted from AF, and this processing is ended.

Therefore, when the air-fuel ratio of the exhaust gas changes from lean to rich as shown in FIG.
During time t ₂ ), the feedback correction coefficient FAF is rapidly reduced by the skip value S, and if the lean state continues thereafter, the feedback correction coefficient FAF gradually decreases as the step value K is subtracted.

Thus, the feedback correction coefficient FAF
Changes its value according to the air-fuel ratio detected by the O ₂ sensor 41. Then, for example, if the rich state continues, the value is gradually reduced to reduce the fuel injection amount, and when the fuel flow is reversed from rich to lean, the value is updated to increase the fuel injection amount.

Therefore, if the reference fuel injection amount is calculated with appropriate accuracy, the target air-fuel ratio can be realized with high accuracy by multiplying FAF and adding a correction to correct the fuel supply amount. The value is controlled to a value, and as a result, it becomes possible to secure excellent air-fuel ratio accuracy.

By the way, the internal combustion engine 10 of the present embodiment is provided with the evaporation purge system 22 as described above,
Fuel is purged from the canister 21 under appropriate operating conditions. In this case, if only the air-fuel ratio feedback control is used, the feedback coefficient FAF
Is required to be controlled with an unreasonably large width, and an appropriate air-fuel ratio accuracy cannot be maintained.

That is, in such a situation where the purge is performed, the air-fuel ratio feedback control should be executed after subtracting the amount supplied by the purge from the reference fuel injection amount.

When it is necessary to make such a correction for the fuel injection amount, it is convenient to perform a constant purge rate control in which the purge flow rate is a constant ratio with respect to the intake air amount. This is because if the purge flow rate is constant, the concentration of the fuel purged in the intake air will also be constant, and appropriate reduction correction can be realized simply by multiplying the reference fuel injection amount by a predetermined constant coefficient.

As described above, when the air-fuel ratio control is conventionally performed in the internal combustion engine having the evaporative purge system, it is the reason why the fuel injection amount reduction correction is performed after the purge flow rate is controlled to the constant purge rate. Therefore, such a correction method is extremely effective when the purge rate can be appropriately maintained at a constant purge rate.

However, it is not always easy to maintain the purge rate constant in the internal combustion engine. That is,
If the intake air amount sharply increases at time t _{1 and} the intake air amount sharply decreases at time t ₂ as shown in FIG. 8A, in order to maintain a constant purge rate, As shown by the broken line, the purge flow rate also needs to rapidly increase at time t ₁ and rapidly decrease at time t ₂ .

However, in the structure in which the purge control valve 27 disposed in the purge passage 26 is appropriately controlled to control the purge flow rate as in the internal combustion engine 10 of this embodiment, the purge flow rate is increased at time t _1. Even if you issue a command to do so,
The purge flow rate does not increase at least until the purge control valve 27 responds.

Even if the purge control valve 27 responds, after the increased purge fuel has passed through the purge control valve 27,
Until the air is actually taken into the internal combustion engine 10, the change in the purge rate in the intake air has no substantial meaning.

Further, since the canister 21 communicating with the purge passage 26 acts as a large intake resistance, the desired purge flow rate cannot be immediately obtained even after the purge control valve 27 responds, and its increasing characteristic. Indicates a transient characteristic with an appropriate time constant.

For this reason, the flow rate of the purge fuel actually flowing into the internal combustion engine 10 should fluctuate with a delay from the ideal fluctuation curve (the curve shown by the broken line), as shown by the solid line in FIG. 8B. Then, as shown in FIG. 8C, the purge rate cannot be maintained at a constant value.

In this case, if the fuel injection is performed according to the fuel injection amount corrected on the premise of the constant purge rate, FIG.
As indicated by the solid line in (D), the air-fuel ratio greatly deviates from the target air-fuel ratio, which deteriorates the air-fuel ratio control accuracy.

Such a problem is caused by the assumption that the purge rate is constant.
The actual purge flow rate indicated by the solid line in (B) is detected, the actual purge rate is calculated based on the detected value and the actual intake air amount shown in FIG. 8 (A), and the fuel is determined according to the actual purge rate. This is a problem that can be solved if the injection amount is corrected.

The air-fuel ratio control system of the present embodiment pays attention to this point, and in consideration of the response delay of the change in the purge flow rate, the actual purge flow rate, that is, the actual purge rate is estimated and the appropriate fuel injection amount is estimated. It was devised to correct the. The processing contents executed by the CPU 34 in order to exert such a function will be described below.

The control of the fuel injection amount in the apparatus of this embodiment is executed by controlling the duty of the fuel injection valve 14. Therefore, the fuel supplied to the internal combustion engine 10 corresponds to the time when the fuel injection valve 14 is open. Therefore, in the following description, the reference fuel injection amount is represented by the reference fuel injection time TAU, and the corrected fuel injection amount is represented by TAU ′ for convenience.

FIG. 5 shows a flow chart of a purge control routine executed to control the purge control valve 27.
It should be noted that this routine is an interrupt routine that is activated every predetermined time, for example, every 16 ms.

When the routine shown in the figure is started, first, at step 100, the target purge rate is calculated. The target purge rate may be set appropriately according to the operating state of the internal combustion engine 10, and may be set to a plurality of values or a fixed value.

After the target purge rate is calculated in this way, the routine proceeds to step 102 to calculate the purge flow rate that can realize the target purge rate. Here, the purge flow rate is calculated by multiplying the target purge rate by the intake air amount QA calculated based on the detection values of the intake pressure sensor 17 and the water temperature sensor 39.

When the purge flow rate to be realized is calculated, the duty ratio that allows the purge flow rate to flow is calculated and the drive circuit 45 is calculated in step 104.
The purge control valve 27 is duty-driven via.

Here, the above steps 100 to 104
Corresponds to the target purge flow rate calculation means 3 and the purge flow rate control means 5b described above. By performing such processing, the purge control valve 27 exhibits the operation corresponding to the broken line in FIG. 8 (B).

When the purge control valve 27 is driven at an appropriate duty ratio in this way, the routine proceeds to step 106, where the purge flow rate calculated this time is the latest purge flow rate data P.
It is stored in the RAM 33 as RGFR0 and the processing of this time is ended.

In this case, the RAM 33 stores the purge flow rate data calculated over the past predetermined period, and according to the present embodiment, the purge flow rate data PRGFR0-PGRFR0 is reversed every 16 ms until 192 ms before. PRGFR12
Is remembered. Therefore, according to these data,
It is possible to read not only the current purge flow rate that can pass through the purge control valve 26 but also the purge flow rate that can pass through the purge control valve 26 at a desired time up to 192 ms before.

The processing contents of correcting TAU using these purge flow rate data will be described below with reference to the flowchart of the TAU correction routine shown in FIG.

When the process shown in FIG. 6 is started, first, at step 200, the long-term average air-fuel ratio correction coefficient FAFSM is calculated by the following formula based on the feedback correction coefficient FAF.

FAFSM = FAFSM + (FAF−FAFSM) / N (1) In the equation (1), FAFSM on the right side is the value calculated in the previous routine processing, and FAF is the feedback correction coefficient described above. It shows the rounding constant.

That is, the FAFSM subtracts the previously calculated FAFSM from the current FAF and subtracts this from the smoothing constant N.
The value calculated by dividing by
It is the value added to FSM. That is, FAFSM is a value obtained by averaging a relatively large period of FAF.

Therefore, when the air-fuel ratio in the internal combustion engine 10 is accurately maintained near the stoichiometric air-fuel ratio, FAFSM
The value of is close to 1.0, and FAFSM is smaller than 1.0 when the air-fuel ratio is biased to the rich side, and the FAFSM value is 1. when the air-fuel ratio is biased to the lean side as a whole.
The value is greater than 0. That is, the FAFSM value represents how much the air-fuel mixture supplied to the internal combustion engine 10 deviates from the stoichiometric air-fuel ratio when observed in a relatively long engine.

After the FAFSM is obtained in this way, it is then determined in step 202 whether or not the value of | FAFSM-1.0 | exceeds a predetermined value, for example, 0.02. This is to determine whether the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10 exceeds a predetermined level and is biased toward the fuel rich side or the fuel lean side.

When it is determined that the air-fuel ratio is biased beyond the predetermined level, the routine proceeds to step 204, where the purge fuel concentration coefficient FGPG per unit purge rate is updated according to the following equation.

FGPG = FGPG + (FAFSM-1.0) / (purge rate) (2) In the above equation (2), FGPG on the right side is a purge fuel concentration coefficient per unit purge rate calculated in the previous learning control routine. Yes, FAFSM is calculated in step 200.

Further, the purge rate in the equation (2) is the target purge rate calculated in step 100 in the routine shown in FIG. 5, and when the purge flow rate reaches the steady state, the purge control valve It is a value equal to the ratio of the purge flow rate determined by the opening degree of 27 and the intake air amount estimated from the output of the intake pressure sensor 17.

In this FGPG, the higher the purge rate, the larger the air-fuel ratio when the fuel is purged, and the more biased the air-fuel ratio is toward the rich side, that is, there is a linear relationship between the purge rate and the value of | FAFSM-1.0 |. This is a learning value introduced with a focus on 1.0, and is a concept that represents the degree of deviation of the air-fuel ratio per unit purge rate, centering on 1.0.

That is, when the fuel is purged at a predetermined purge rate, the air-fuel ratio is biased toward the rich side, and (FAFSM-
If (1.0) / (purge rate) becomes a negative value, FGPG that was 1.0 at the initial time becomes a value smaller than 1.0 by the deviation of the air-fuel ratio per unit purge rate.

In step 202, | FAF
The configuration in which the SM-1.0 | is updated only when the value exceeds a predetermined value α (for example, 0.02) may cause a temporary change in the calculated value of FAFSM due to the influence of disturbance or the like. This is to prevent the influence from being reflected in FGPG.

After the FGRG is updated to the proper value in this way, the processing for realizing the actual purge rate estimating means M1 described above is performed in steps 206 to 214.

First, at step 206, a delay time from when a predetermined drive signal is issued to the purge control valve 27 until the purge flow rate corresponding to the drive signal reaches the internal combustion engine 10 (time t _{1 to} T in FIG. 8). ₁ or time t ₂ ~ T
Equivalent to ₂ ) is calculated. This delay time is a value obtained by adding the response delay time specific to the purge control valve 27 and the time required for the purge fuel to reach the internal combustion engine 10 after passing through the purge control valve 27.

Here, from the purge control valve 27 to the internal combustion engine 1
The negative pressure state in the intake manifold 12, that is, the engine speed Ne is greatly involved in the time required to flow to 0, and this delay time is eventually N as shown in FIG. 7 (A).
It can be obtained as a function of e. Therefore, in this embodiment, the map shown in FIG. 7A is stored in advance in the ROM 32, and the delay time is calculated with reference to this map.

In step 208, based on the delay time thus obtained and the purge flow rate data stored in the routine shown in FIG. 5, the purge flow rate tPR that would have passed through the purge control valve 27 before the delay time was reached.
The GFRj is read from the RAM 33. This is because the purge flow rate is considered to be contained in the intake air that is about to be supplied to the internal combustion engine 10.

However, in the process in which the purge fuel that has passed through the purge control valve 27 flows through the purge passage 26, the surge tank 15 and the intake manifold 12, the fluctuation of the purge flow rate tends to be smoothed. Therefore, in order to accurately estimate the purge flow rate contained in the intake air which is about to be drawn into the internal combustion engine 10, the purge flow rate data tPRGF read in step 208 is read.
It is necessary to adjust Rj appropriately.

The reason why the smoothing number N is calculated in step 210 is to pay attention to this point, and after calculating the appropriate smoothing number N, the actual purge flow rate PRGFRSM is calculated in step 212 according to the following equation. To do.

PRGFRSM = PRGFRSM + (tPRGFRj−PRGFRSM) / N (3) Here, PRGFRSM on the right side is the actual purge flow rate calculated in the previous processing. That is, PRG
FRSM is a value obtained by averaging the actual purge flow rate for a long period using the number N of smoothing.

The smoothing number N is switched depending on whether the internal combustion engine 10 is in an accelerating state or a decelerating state,
Alternatively, as shown in FIG. 7 (B), it is preferable to adopt a configuration or the like that calculates as a function of the engine speed Ne, and to appropriately calculate according to the operating state of the internal combustion engine 10, but it is also possible to process as a constant. is there.

In this way, the actual purge flow rate PRGFRS
After calculating M, in step 214, the actual purge rate PRGRSM is calculated according to the following equation.

PRGRSM = PRGFRSM / QA (4) Here, PRGFRSM on the right side is the above step 2
12 and the QA is the intake pressure sensor 1
The value of the intake air amount calculated based on the detection signal of No. 7 is used.

In this way, steps 206 to 214 described above are performed.
Realizes a process corresponding to the actual purge rate estimating means M1 described above, and the actual purge rate PRGRSM calculated in step 214 is the ratio of the purge flow rate and the intake air amount at the stage of actually being sucked into the internal combustion engine 10. Will be represented.

By the way, the FGRG calculated in the above step 204 represents the degree of deviation of the air-fuel ratio per unit purge rate around 1.0, and when the air-fuel ratio is deviated to the fuel rich side, the value is smaller than 1.0. As described above, the coefficient is

Therefore, the result value of the calculation of (FGPG-1) represents the magnitude of the deviation of the air-fuel ratio per unit purge rate centered on 0, and its sign is that the air-fuel ratio is on the fuel rich side. When it is biased to, it means negative, and when it leans to the fuel lean side, it means positive.

Therefore, the result value of the calculation of (FGPG-1) × (actual purge rate) represents the magnitude of the air-fuel ratio deviation due to the actual fuel purge, and the sign thereof is the air-fuel ratio rich side. It also indicates which direction the lean side is offsetting.

Then, using this concept, FPRG = 1-
If a coefficient of (FGRG-1) x (actual purge rate) is configured, FPRG is small around the fuel rich side with 1.0 as the center, large when biased toward the fuel lean side, and actually purged. A coefficient that fluctuates in a width corresponding to the deviation of the air-fuel ratio according to the rate is formed.

Therefore, if the reference fuel injection time TAU is multiplied by using this coefficient as a correction coefficient, the corrected fuel injection time TAU 'has a small actual purge rate and a small amount of fuel supplied by the fuel purge. In some cases, the value is long, and when the actual purge rate is large and the fuel supply amount by the fuel purge is large, the value is corrected shortly.

Therefore, in the present embodiment, when the actual purge rate is calculated in step 214, step 2
The routine proceeds to step 16 to calculate the correction coefficient FPRG as in the following equation (5), and then in step 218, the correction coefficient FPRG is used to correct the fuel injection time TAU as in the following equation (6).

FPRG = 1 + (FGPG-1) × (actual purge rate) (5) TAU ′ = TAU × FPRG (6) These steps 216 and 218 are the fuel injection amount calculation means described above. Equivalent to M2.

As described above, in the air-fuel ratio control system of this embodiment, when the fuel purge by the evaporative purge system 22 is performed, the actual purge rate is estimated to estimate the fuel injection time TA.
U is corrected, and the variation of the purge rate is reflected in the correction coefficient. Therefore, an appropriate air-fuel ratio can always be ensured even when the actual purge rate greatly varies depending on the operating state of the internal combustion engine.

In the apparatus of the present embodiment, the case where it is used together with the feedback control for the purpose of improving the air-fuel ratio control accuracy is illustrated, but the present invention is not limited to this, and for example, the purge rate and the correction coefficient of TAU can be used. May be stored in advance as a map, and the correction coefficient value may be determined by referring to the map with the actual purge rate estimated as described above.

When such a configuration is adopted, the control content can be simplified, the air-fuel ratio deviation due to the fluctuation of the actual purge rate can be appropriately prevented, and it is much simpler than the above-mentioned embodiment apparatus. Can be realized.

By the way, the air-fuel ratio control system of the above-described embodiment has a configuration in which when the operating state of the internal combustion engine 10 changes, the amount of fuel supplied from the fuel injection valve 14 is corrected to cancel the excess purged fuel. is there. Therefore, in order to enjoy the effect, it is premised that the fuel injection valve 14 is injecting a sufficient amount of fuel that can offset the excessive purge fuel at the transition time.

However, in the internal combustion engine 10 having the function of electronically controlling the fuel injection amount as shown in FIG. 4, the structure for cutting the fuel injection is generally executed under a predetermined operating condition for the purpose of improving fuel consumption. There is. When such a fuel cut is executed, there is no fuel functioning as a buffer for canceling the excess amount of purge fuel in the air-fuel ratio control device having the above configuration, and the purge control valve 2
7 is a control delay and a purge control error due to the flow time of purge fuel is a problem.

Even if the fuel cut execution condition is satisfied and the purge control valve 27 is fully closed, the purge control valve 27 is already closed.
After passing through the fuel cell, the purge fuel that is in the process of flowing toward the internal combustion engine 10 and the purge fuel that flows when the control of the purge control valve 27 is delayed will be supplied to the internal combustion engine 10 after the fuel cut command is issued. Because.

By the way, the fuel cut in the internal combustion engine is generally executed in accordance with the time chart shown in FIG. That is, in the fuel cut, the throttle opening is suddenly fully closed as shown in FIG.
_{0 to} t ₁ ) is _one of the execution conditions, and is executed while the engine speed NE drops near the idle speed.

Here, FIG. 11B shows how the intake air amount decreases with the throttle opening (the same applies to the basic fuel injection amount TAU calculated based on the intake air amount). Time t when the opening becomes "0"
_{From 1} onward, the amount of intake air or the amount of fuel injection that can maintain the idle speed is converged.

Further, FIG. 11C shows the state of the idle ON fuel cut flag which shows the satisfaction of the execution condition of the fuel cut, and the fuel cut is executed at the same time when the throttle opening becomes "0". In view of the fact that the impact is generally large and the riding comfort of the vehicle deteriorates, it is set to be turned on on condition that a predetermined delay time has elapsed after time t ₁ when the throttle opening becomes “0”. It was done.

That is, in the internal combustion engine according to the time chart shown in FIG. 11, the fuel injection amount equivalent to that in the idling state is set between time t _{1 and} t ₂ , and the time t
After ₂ , the fuel injection amount is set to “0” regardless of the calculated value shown in FIG. 11 (B).

By the way, when the evaporative purge system 22 is provided like the internal combustion engine 10 of the present embodiment, it is effective to cut off the purged fuel when the fuel is cut off, in order to enhance the effect.

In this case, the purge control 27 is driven by the duty drive voltage (VSV voltage) as shown in FIG. 11 (E). Therefore, depending on the timing at which the idle ON fuel cut flag is turned on, a signal may be continuously issued until the time t ₃ to open the purge control valve 27 thereafter.

After the fluctuation of the VSV voltage and before the purge rate actually changes, the control delay time of the purge control valve 27 is required as shown in FIG. Will be fully closed after the elapse of these times, that is, at time t ₄ shown in FIG.

Further, considering the flow time until the purge fuel passes through the purge control valve 27 and reaches the internal combustion engine 10, as shown in FIG. 11 (F), the VSV voltage has the flow time at the time t _4. It can be considered that the fuel cut is followed at the time t ₅ obtained by adding the above, and the purging of the purge fuel is continued for a long period from the time t _{2 at} which the purge fuel should be cut to the time t _5. Become.

As described above, in the internal combustion engine provided with the evaporative purge system 22, it is difficult to cut off the purged fuel at an appropriate timing when the fuel is cut, and a high duty ratio is set especially when the fuel cut is executed. In addition, when the fuel concentration in the purge gas is high, the air-fuel mixture may temporarily become rich and the exhaust emission may be deteriorated as the intake air amount sharply decreases.

Therefore, in such a case, it is appropriate to shorten the delay time after the throttle opening becomes "0" until the idle ON fuel cut flag is turned on.

That is, for example, when the throttle opening is suddenly closed and fully closed as shown in FIG. 12 (FIG. 12A).
If the idle ON fuel cut flag is turned on at the same time as the full closing at time T _{1 in the} middle (FIG. 12).
(B)) At time T ₁ , the fuel cut is reflected in the purge fuel at time T _4, which is the sum of the delay due to the duty frequency of the purge VSV voltage, the control delay of the purge control valve 27, and the flow time of the purge fuel. be able to.

Further, even if the fuel cut is executed at the time T ₁ , the purge fuel which has achieved the high purge rate is continuously supplied to the internal combustion engine 10 until the time T ₄ , and the delay time is set. Even if there is not, no unreasonable impact will occur due to the fuel cut.

Therefore, in the air-fuel ratio control system of this embodiment, the delay time set at the time of fuel cut is
The purge rate realized at that time was made variable so as to improve the exhaust emission at the time of fuel cut without deteriorating the riding comfort.

FIG. 13 is a flow chart of a fuel cut routine executed by the electronic control unit 30 to realize such a function. The electronic control unit 30 executes this routine to execute the fuel cut command means 8 and the conditions described above. The determination means M5 is realized.

When the processing shown in FIG. 13 is started, first, in step 400, in step 20 of the routine shown in FIG.
It is checked whether the FGPG calculated in 4 is less than the predetermined judgment value F ₁ .

Considering that the delay time at the time of fuel cut should be set on the basis of the magnitude of the influence of the purge fuel on the operating state of the internal combustion engine 10, the magnitude of such an influence is determined by the unit purge rate. Purge fuel concentration coefficient FGP
It is intended to judge by the value of G.

In this case, when FGPG ≦ F ₁ is established, it can be determined that the presence or absence of the purged fuel has a great influence on the operating state of the internal combustion engine 10.
When PG ≦ F ₁ is not established, it can be determined that the presence or absence of purge fuel does not significantly affect the operating state of the internal combustion engine 10. In this sense, in this embodiment, the purge rate estimating means M3 described in step 204 in FIG. 6 is used.
Equivalent to.

After the above determination, if the above condition is satisfied, the process from step 402 onward is performed, and if the condition is not satisfied, the process from step 410 onward is performed. In this case, steps 402 and 410 are steps for determining whether the IDL signal indicating the fully closed state is supplied from the throttle switch 38 which detects the state of the throttle valve 19.

Here, if the IDL signal is not supplied, the fuel cut processing should not be executed in the internal combustion engine 10, and the processing of this time is ended together.

On the other hand, when the IDL signal is detected in step 402 or 410, the process proceeds to step 404 or 412, respectively, and the engine speed NE is set to the predetermined rotation speed based on the detection signal of the crank angle sensor 43. Number N
Determine if it is ₁ or more. This is because the fuel cut should be executed only in the area where the engine stall does not occur, and it is possible to determine the possibility.

Therefore, when NE ≧ N ₁ is not established, it is determined that the fuel cut is not to be executed, and the current processing is ended as it is, and the fuel cut is executed only when such a condition is established. Step 406, respectively
Or proceed to 414. In this sense, in this embodiment,
The throttle switch 38 and the crank angle sensor 43 correspond to the above-mentioned driving state detecting means M4.

Steps 406 and 414 are steps to secure the delay time according to each case according to the judgment made in the above step 400. That is, step 406 is a step of counting the delay time T ₀ set to a relatively short time when FGPG ≦ F ₁ is satisfied (when the influence of purge fuel is large), and step 414 is FGPG ≦. This is a step of counting the delay time set for a relatively long time when F _{1 is} not established.

In this embodiment, the setting condition is T ₁ > T ₀ . Therefore, when step 406 is executed, the condition is satisfied in a relatively short time after the IDL signal is turned on, that is, after the throttle valve 19 is suddenly closed and fully closed, and step 408 is executed. To be executed. On the other hand, when step 414 is executed, after the IDL signal is turned on, step 408 is executed after a relatively long delay time. It is also possible to set "0" as T ₀ .

Here, step 408 is a step corresponding to the fuel cut command means 8 described above, and a step of commanding fuel cut to the fuel injection valve 14 and the purge control valve 27, specifically, idle ON. This is a step in which the fuel cut flag is turned on and fuel cut is executed.

Thus, in this embodiment, IDL
The fuel cut is executed on condition that the signal is turned on, the engine speed NE> N ₁ , and the delay time T ₀ or T ₁ set based on the value of FGPG is elapsed. In this sense, the above steps 400-
Reference numerals 406 and 410 to 414 denote the condition determination means M described above.
Equivalent to 5.

As a result, when the purge fuel has a large influence on the internal combustion engine 10 to the extent that FGPG ≦ F ₁ is satisfied, the time chart shown in FIG. 12 is satisfied and the impact due to the fuel cut is not caused. When the exhaust emission is improved and the influence of the purge fuel is small to the extent that FGPG ≦ F ₁ is not established, the time chart shown in FIG. 11 is established, and there is no impact and good exhaust gas is obtained. A fuel cut that can secure emission will be realized.

As described above, the air-fuel ratio control system of the present embodiment can always ensure good exhaust emission even when the fuel cut is executed.

In the above embodiment, one of the fuel cut execution conditions is that the throttle opening is "0", that is, that the IDL signal is supplied from the throttle switch 38. The present invention can also be applied to the case where the value calculated as the injection amount TAU is equal to or larger than the predetermined value TAUmin as one of the execution conditions.

That is, as described above, when the throttle opening is suddenly closed as shown in FIG. 14A, the basic fuel injection amount TAU is reduced as shown in FIG. 14B. If the TAU is reduced to a value equal to or less than the predetermined determination value TAUmin, it is determined that the internal combustion engine 10 is not required to have a driving force, and the driver can perform the fuel cut before the throttle valve 19 is fully closed. There is nothing against the intention of.

In this case, the judgment value TAU depends on the purge rate.
If min is increased or decreased, the time when the idle ON fuel cut is turned on is variable, and the same effect as when the delay time is variable can be obtained.

FIG. 15 is a flowchart of another example of the fuel cut routine for correcting the influence of the purged fuel at the time of fuel cut from this viewpoint. In the figure,
Steps that execute the same processing as the routine shown in FIG. 13 are designated by the same reference numerals, and the description thereof will be omitted.

That is, in this routine, FGP
The magnitude of the influence of the purge fuel on the internal combustion engine 10 is determined based on the value of G. If the result is that the purge fuel has a great influence, the routine proceeds to step 416, where a comparatively large determination value TAUmin1 and TAU are compared. And TAU ≤ TAU
If min1 is satisfied, fuel cut is executed, and if the effect of purge fuel is small, the routine proceeds to step 418, where a comparatively small judgment value TAUmin2 and TAU are compared, and T
The fuel cut is executed only when AU ≦ TAUmin2 is satisfied.

In this case, when the purged fuel has a great influence, the fuel cut is executed relatively early, and the excess fuel due to the purge fuel control error is the fuel necessary for alleviating the impact at the time of the fuel cut. As a result, it always balances good ride comfort and exhaust emission.

As described above, when the electronic control unit 30 executes this routine, a good effect can be obtained even when the logic for executing the fuel cut before the throttle valve 19 is fully closed is adopted. You can

FIG. 16 is a block diagram of an air-fuel ratio control system according to another embodiment of the present invention. The air-fuel ratio control device shown in FIG.
In addition to the device shown in FIG. 4, it is characterized in that an ISCV (idle speed control valve) 50 and a drive circuit 51 for driving the same are provided in order to realize the dashpot mechanisms 9a and 9b.

The ISCV 50 has a suitable amount of air when the throttle valve 19 is fully closed, that is, when the internal combustion engine 10 is in the idling state.
Is provided to realize an appropriate idling state by bypassing and circulating, and is duty-driven based on the drive signal generated by the drive circuit 51.

By the way, when the internal combustion engine is operating at a high load, if the throttle valve 19 is fully closed and no air is supplied to the internal combustion engine 10 thereafter, the internal combustion engine 10 is severely braked. , The riding comfort of the vehicle is significantly deteriorated. For this reason, an internal combustion engine is generally provided with a dashpot mechanism, that is, a mechanism for continuing air flow for a predetermined period of time after the driver fully closes the accelerator pedal.

Here, in the engine including the ISCV 50 such as the internal combustion engine 10 shown in FIG. 16, the dashpot mechanism can be realized by the ISCV 50 in view of the small amount of air to be circulated by the dashpot mechanism. .

That is, when the throttle valve 19 is fully closed by the driver's operation, a sufficient amount of air for cushioning the impact is circulated through the ISCV 50 after the throttle valve 19 is fully closed. If you do
The dashpot mechanism will be realized. And
The flow rate of air required for shock absorption can be grasped as a function of the intake air amount GN supplied to the internal combustion engine 10 immediately before the throttle valve 19 is fully closed.

Therefore, in the present embodiment, the duty ratio of the drive signal supplied to the ISCV 50 to realize the dashpot mechanism is set as a map in relation to the intake air amount GN, and the map is set as necessary. Based on I
It was decided to realize a dashpot mechanism by driving the SCV50.

FIG. 17 shows an example of the driving method. In FIG. 17 (A), the initial value DDP1 set by the map at time t ₁ is maintained for a predetermined time, and then at a preset damping speed. An example of converging is shown in FIG.
Set the initial value DDP1 at time t _1, in which then shows immediately the examples to converge at a predetermined decay rate, respectively.

When such processing is executed, DD in FIG.
The air corresponding to the area surrounded by the P waveform is supplied toward the internal combustion engine 10 after the throttle valve 19 is fully closed, and the impact of the engine brake is mitigated to maintain good driving characteristics.

By the way, as described above, if the throttle valve 19 is suddenly closed while the fuel is being purged, the purged fuel excessively becomes transient. As described above, the air-fuel ratio control apparatus shown in FIG. Is for canceling the excessive purged fuel by the fuel injection amount or the fuel cut time.

Here, the reason why the excess purged fuel becomes a problem when the throttle valve 19 is fully closed is that the excess mixture temporarily enriches the air-fuel mixture, and the exhaust emission deteriorates accordingly. Therefore, when the purged fuel becomes excessive, if it is possible to circulate the amount of air corresponding to the excessive purged fuel, it is possible to prevent the exhaust emission from deteriorating.

The air-fuel ratio control system of the present embodiment is characterized in that the deterioration of exhaust emission due to the full closing of the throttle valve 19 is prevented by paying attention to such a point. Specifically, as shown in FIG. 18, the electronic control unit 30 displays the duty ratio map (DDP1) corresponding to a small purge rate and the duty ratio map (DDP2) corresponding to a large purge rate. It is characterized in that the dashpot routine shown in 19 is executed.

That is, when the routine shown in FIG. 19 is started, first, at step 500, the magnitude of the influence of the purge fuel on the internal combustion engine 10 is judged based on the value of FGPG, and when the influence degree is small (FGPG ≦ F _{If 1 is} not satisfied), the process proceeds to step 502, and if the degree of influence is large (FGPG ≦ F _{1 is} satisfied), the process proceeds to step 510.

Steps 502 and 510 are steps for determining whether the elapsed time after the IDL signal is turned on is less than the predetermined time T ₁ . As described above, the air-fuel ratio control system according to the present embodiment has the I
DDP as the initial duty ratio of the drive signal of SCV50
1 is used or DDP2 is used. The selection is made when the initial duty ratio is set,
That is, it should be executed only immediately after the throttle valve 19 is fully closed, and the timing is set by the time T ₁ after the IDL signal is turned on.

Then, only when it is determined that the conditions are satisfied in the above steps 502 and 510, step 50
The process proceeds to 4, 512 to search the map shown in FIG. As a result, a relatively small initial duty ratio DDP1 is set when the purged fuel does not significantly affect the operating state of the internal combustion engine 10, and a relatively large initial duty ratio is set when the purged fuel has a large effect. become.

Upon completion of these processes, the process proceeds to step 506 or 514, respectively, and thereafter, the processes in and after step 500 are repeatedly executed until a predetermined time T ₂ has elapsed after the IDL signal was turned on. As shown in FIG. 17A, during this period, the ISCV50 has an initial duty ratio DD.
This is for supplying a drive signal for P1 or DDP2.

When T ₂ has passed, the process proceeds to step 508 or 516, respectively, to attenuate the duty ratio of the ISCV50 drive signal. That is, step 508
At step 516, the predetermined value X ₁ is subtracted to obtain a new duty ratio at every execution of this step, and at step 516, the predetermined value X ₂ is subtracted at every execution of this step to set a new duty ratio.

In this case, in this embodiment, the steps
X corresponding to the attenuation width at 508 ₁And step 516
X corresponding to the attenuation width at₂Between and X₁≧ X₂of
The relationship is established. Therefore, the effect of purged fuel is small.
In step 508 which is executed when the
Attenuation is performed and the effect of purge fuel is small
In step 516, the damping is performed with a small width.
become.

As described above, according to the air-fuel ratio control apparatus of this embodiment, when the fuel purged by the evaporative purge system 22 has a great influence on the operating state of the internal combustion engine 10, when the throttle valve 19 is fully closed. When a relatively large amount of air is supplied through the ISCV 50 while the purged fuel does not significantly affect the operating state of the internal combustion engine 10, a relatively small amount of air is fully closed when the throttle valve 19 is fully closed. Are distributed through ISCV50 and supplied.

Therefore, the purge fuel supplied at the time of fuel cut due to the control delay of the purge control valve 27 and the like, and I
This has the effect that the amount of air flowing through the dashpot mechanism by the SCV 50 is matched, and as a result, good exhaust emission can always be maintained.

Incidentally, in the embodiment shown in FIG.
Although the dashpot is electrically realized by using the ISCV50, a mechanical dash that delays the throttle valve 19 from being fully closed after the accelerator pedal is fully closed to secure a desired air amount. It is also possible to obtain the same effect as in the above embodiment by using a pot.

FIG. 20 is a block diagram of the dashpot 60 which realizes such a function. That is, the dashpot 60 includes a rod 61 that presses the valve body of the throttle valve 19 in the valve opening direction, a spring 63 that biases the rod 61 via the diaphragm 62, and a negative pressure chamber 64. In this case, if the negative pressure chamber 64 is connected to the downstream side of the throttle valve 19 in the intake passage 16, the rod 6 will increase as the throttle opening becomes smaller and the intake negative pressure increases.
The force of 1 pressing the throttle valve 19 weakens, and the opening of the throttle valve gradually decreases.

Here, in this embodiment, as shown in FIG. 20, the switching valve 6 is provided between the negative pressure chamber 64 and the intake passage 16.
5, a small orifice 66 and a large orifice 67 are provided. Then, if the switching valve 65 communicates the intake passage 16 and the negative pressure chamber 64 via the small orifice 66, a relatively large amount of air is generated after the accelerator pedal is fully closed.
If the air flows through the large orifice 67 and is communicated with the large orifice 67, the amount of the air becomes relatively small, and as a result, the amount of the air flowing through the dash pot 60 becomes variable, as in the case of using the ISCV50. .

Therefore, the dashpot 60 having such a structure
When the purged fuel has a large influence on the internal combustion engine 10, the switching valve 16 is switched to the small orifice 66, and when the influence of the purged fuel is large, the switching valve 16 is switched to the large orifice 67. With the switching configuration, the same effect as that of the air-fuel ratio control device shown in FIG. 16 can be secured.

[0173]

As described above, according to the first aspect of the invention, the actual purge rate is estimated when the fuel is purged from the canister to the internal combustion engine, and the actual purge rate should be supplied to the internal combustion engine. The amount of fuel is corrected. Therefore, the air-fuel mixture supplied to the internal combustion engine can be appropriately controlled to the target air-fuel ratio, even though the actual purge rate varies depending on the operating condition of the internal combustion engine.

Therefore, according to the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, unlike the conventional air-fuel ratio control apparatus, the air-fuel ratio of the air-fuel mixture is changed every time the intake air amount changes and the actual purge rate changes. It has the features that the fuel economy of the internal combustion engine and the exhaust emission can be improved without significantly deviating from the target value.

According to the second aspect of the present invention, if a high purge rate is ensured during execution of fuel cut, the delay time at fuel cut is set short, and if the purge rate is low, the delay time is set long. Therefore, regardless of the amount of purged fuel from the canister, the amount of fuel supplied after the internal combustion engine is in a state where fuel cut should be executed is always the amount necessary and sufficient to mitigate the impact due to fuel cut. . Therefore, there is a feature that exhaust emission can be improved without deteriorating a smooth operating state at the time of fuel cut.

Further, according to the third aspect of the present invention, when the throttle valve is rapidly closed, the amount of purge fuel supplied to the internal combustion engine is delayed due to the control of the purge flow rate control means or the flow time of the purge fuel. On the assumption that the change cannot be followed due to this, the dashpot mechanism secures an amount of air corresponding to the purged fuel supplied after the throttle valve is rapidly closed.

Therefore, according to the air-fuel ratio control system for an internal combustion engine of the present invention, the air-fuel mixture supplied to the internal combustion engine does not become rich even when the throttle valve is suddenly closed, which is good even in such a situation. It has the feature that various exhaust emissions can be secured.

[Brief description of drawings]

FIG. 1 is a principle diagram of an air-fuel ratio control device for an internal combustion engine according to a first aspect of the invention.

FIG. 2 is a principle diagram of an air-fuel ratio control device for an internal combustion engine according to a second aspect of the invention.

FIG. 3 is a principle diagram of an air-fuel ratio control device for an internal combustion engine according to a third aspect of the invention.

FIG. 4 is an overall configuration diagram of an internal combustion engine including an air-fuel ratio control device that is an embodiment of the present invention.

FIG. 5 is a flowchart of an example of a purge control routine executed by the electronic control unit of the apparatus of this embodiment.

FIG. 6 is a flowchart of an example of a fuel injection time (TAU) correction routine executed by the electronic control unit of the present embodiment device.

FIG. 7 is an example of a map used for a fuel injection time (TAU) correction routine.

FIG. 8 is a time chart showing a change state of a purge rate and the like at the time of fuel purging.

FIG. 9 is a routine for calculating an air-fuel ratio feedback coefficient FAF.

FIG. 10 is a time chart showing a relationship between an air-fuel ratio of exhaust gas and a feedback correction coefficient FAF.

FIG. 11 is a time chart for explaining the occurrence of a purge fuel control error.

FIG. 12 is a time chart (No. 1) for explaining the operation of the air-fuel ratio control device of the present embodiment.

FIG. 13 is a flowchart of an example of a fuel cut routine executed by the electronic control unit of this embodiment.

FIG. 14 is a time chart (No. 2) for explaining the operation of the air-fuel ratio control device of the present embodiment.

FIG. 15 is a flowchart of another example of the fuel cut routine executed by the electronic control unit of this embodiment.

FIG. 16 is an overall configuration diagram of another example of the air-fuel ratio control device according to the present invention.

FIG. 17 is a diagram for explaining the function of the dashpot.

FIG. 18 is an example of a map used when implementing a dashpot mechanism using ISCV.

FIG. 19 is a flowchart of an example of a dashpot routine executed by the electronic control unit of this embodiment.

FIG. 20 is a configuration diagram of an example of a dashpot suitable for realizing the air-fuel ratio control device of the present embodiment.

[Explanation of symbols]

M1 actual purge rate estimating means M2 fuel injection amount calculating means M3 purge rate estimating means M4 operating state detecting means M5 condition determining means M6 circulating air amount varying means 1, 21 canister 2 intake passage 3 target purge flow rate calculating means 4, 26 purge passage 5a, 5b Purge flow rate control means 6, 22 Evaporative purge system 7a, 7b Fuel injection means 9a, 9b Dashpot mechanism 10 Internal combustion engine 12 Intake manifold 14 Fuel injection valve 15 Surge tank 27 Purge control valve 30 Electronic control unit 38 Throttle switch 39 O ₂ sensor 50 ISCV 60 Dashpot 65 Switching valve 66 Small orifice 67 Large orifice

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F02M 23/08 F02M 23/08 A 25/08 301 25/08 301J (72) Inventor ▲ Taka ▼ Mitsuda Toyota, Aichi Prefecture Toyota Town No. 1 Toyota Motor Co., Ltd. (72) Inventor Nobuyuki Kobayashi Toyota Town, Aichi Prefecture Toyota Town No. 1 Toyota Motor Co., Ltd. (56) Reference JP 5-33733 (JP, A) JP 5 -18326 (JP, A) JP 4-292542 (JP, A) JP 4-94444 (JP, A) JP 5-52139 (JP, A)

Claims (3)

(57) [Claims] [1 claim: a canister for storing fuel vapor temporarily the target purge flow rate calculation means for calculating a purge flow amount to be purged into the intake passage in accordance with the operating condition of the internal combustion engine, and the intake passage and said canister A device for controlling an air-fuel ratio of an internal combustion engine, comprising an evaporative purge system comprising a purge flow rate control means for controlling a purge flow rate by controlling conduction of a purge passage communicating with each other. In an air-fuel ratio control device for an internal combustion engine, which injects corresponding fuel into the intake passage by means of fuel injection means , based on a conduction state of the purge passage before a predetermined time.
Te, and actual purge rate estimating means for estimating a ratio of purged fuel in the mixed Aiki that will be sucked into the internal combustion engine, respond to purge rate estimated by said actual purge rate estimating means
The fuel injector to achieve the desired air-fuel ratio.
An air-fuel ratio control device for an internal combustion engine, comprising: a fuel injection amount calculation means for correcting a fuel injection amount according to a step . 2. A canister for temporarily storing evaporated fuel, a target purge flow rate calculating means for calculating an amount of purge fuel to be purged into an intake passage according to an operating condition of an internal combustion engine, the canister and the intake passage. A device for controlling an air-fuel ratio of an internal combustion engine, comprising an evaporative purge system comprising a purge flow rate control means for controlling a purge flow rate by controlling conduction of a purge passage communicating with the internal combustion engine. Fuel injection means for injecting fuel according to the above into the intake passage, and fuel cut command means for commanding the purge flow rate control means and the fuel injection means to cut fuel supply when a predetermined condition is satisfied. In an air-fuel ratio control system for an internal combustion engine, a purge rate estimating means for estimating the ratio of purged fuel in the air-fuel mixture, and an internal combustion engine for executing fuel cut After the operating state detecting means for detecting that the operating state is detected, and the operating state detecting means detects the operating state in which the fuel cut should be executed, the purge rate is determined according to the purge rate estimated by the purge rate estimating means. Is larger, the condition determination means for determining whether or not the execution condition of the fuel cut is satisfied after a delay time set to a shorter time has elapsed, and an air-fuel ratio control device for an internal combustion engine. 3. A canister for temporarily storing evaporated fuel, a target purge flow rate calculation means for calculating the amount of purge fuel to be purged into the intake passage according to the operating condition of the internal combustion engine, the canister and the intake passage. Is equipped with an evaporative purge system consisting of a purge flow rate control means for controlling the purge flow rate by controlling the continuity of a purge passage communicating with the intake passage, and when the throttle valve provided in the intake passage is suddenly closed, Estimate the ratio of purge fuel in the air-fuel ratio of an internal-combustion engine that controls the air-fuel ratio of the internal-combustion engine equipped with a dashpot mechanism that allows an appropriate amount of air to flow in order to prevent a decrease in the intake air amount And a purge rate estimating means for determining the amount of air that the dashpot mechanism circulates when the throttle valve is rapidly closed. Air-fuel ratio control system for an internal combustion engine, characterized in that it comprises a circulation air amount varying means for setting as the estimated value is greater in a large amount.